Devices and methods for monitoring volatile, semi-volatile, or particulate matter in air are highly useful in a wide variety of applications, especially those in which there are public health concerns related to air quality. For example, polycyclic aromatic hydrocarbons (PAHs) are ubiquitous atmospheric pollutants that are a concern due to their toxicity. Investigations of their deposition fluxes are often conducted to assess loadings to terrestrial or aquatic environments that may be at risk. A common approach for estimating deposition of PAHs and other semivolatile air pollutants is based on sampling of ambient air.
Air sampling devices may be categorized as either active or passive air samplers. Active air samplers typically employ pumps to pass air through or over samplers, whereas passive air samplers typically rely on passive processes such as diffusion to sample air.
Three types of passive air samplers are commonly employed. The first, bulk deposition collectors, are continuously open collectors that collect both wet and dry deposition components. Bulk deposition collectors are prone to sampling artifacts (degradation of target analytes exposed to sunlight or revolatilization to air), and are not able to separate dry deposition from wet deposition.
Biomonitoring is a second passive sampling technique that may be employed. In this technique, biomonitors such as pine needles, mosses, and lichens are used to assess deposition. However, this method has associated sources of uncertainty that arise due to inconsistencies with biomonitors as collection substrates. Processes may degrade target analytes following their deposition on biomonitors.
Modeling techniques are a third approach to passive air sampling. Modeling techniques are an indirect approach for assessing deposition using ambient air concentration data and estimated gas- and particle-phase deposition velocities to calculate deposition fluxes. This approach requires information on wind speed, topography, particle-size distribution, and chemical particle-gas partitioning data in order to provide an estimate for deposition flux. This is a data-heavy approach that could result in high uncertainty depending on the availability of data.
One example of a commercially available passive air sampler is the TE-200 PUF passive air sampler (Tisch Environmental, herein referred to by the acronym PAS). The PAS device is a passive air sampler employing a polyurethane foam (PUF) collection media. The PAS device comprises upper and lower fitted bowls joined by a hinge on one side. An assembled PAS device adopts a double dome shape. The upper and lower fitted bowls assemble such that a gap is formed between the rims of the open ends of the two bowls. A PUF collection media is supported within the chamber formed by the fitted bowls. Air circulation may enter and exit the chamber, allowing for passive sampling of the air through exposure to the contained PUF disk.
While the PAS device is useful for a variety of passive air sampling applications, the double-dome chamber design of the PAS device inherently precludes larger depositing particles. In many applications, for example, in the case of polyaromatic hydrocarbon (PAH) sampling, larger particles dominate the dry deposition particle component and thus a passive air sampling device operating in the full size-range of depositing particles would be more desirable.
A variety of other passive air sampling devices are also known, for example, as described and taught in U.S. Pat. No. 7,980,147B2 to Tang.